Pelvic floor disorders affect up to one-third of adult women. One of the most prevalent pelvic floor disorders is pelvic organ prolapse, a condition in which the pelvic organs (bladder, vagina, cervix and uterus) herniate through the vaginal opening. Up to 11% of women have surgery for pelvic organ prolapse or urinary incontinence in their lifetime and more than 225,000 inpatient surgical procedures for pelvic organ prolapse are performed per year in the United States at an estimated annual direct medical cost of over one billion dollars. Although multiple mechanisms have been hypothesized to contribute to the development of pelvic organ prolapse, none fully explain the origin and natural history of this process. Epidemiologic studies indicate that vaginal birth and aging are the two major risk factors for developing pelvic organ prolapse. During the last funding period, we used mouse models of pelvic organ prolapse and tissues from women with and without prolapse to investigate the overall hypothesis of our research program, namely that vaginal wall support is maintained by a delicate balance between the synthesis/assembly and degradation of elastic fibers in the vaginal wall. In this application, we propose to build on this solid foundation to (i understand the relative importance of elastic fiber structural integrity and protease activation in the pathogenesis of pelvic organ prolapse, (ii) investigate the contribution of a novel elastin microfibrillar protein, LTBP4, and TGF? signaling in the pathogenesis of pelvic organ prolapse, and (iii) utilize injectable nanoparticle hydrogels with or without estrogen to prevent or ameliorate development of vaginal prolapse after injury.